The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 101 36 270.6 filed Jul. 25, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a deflection controlled roll having a rotating roll jacket, a rotationally fixed yoke axially passing through the roll jacket, and a plurality of hydrostatic support elements which are arranged in series on the yoke in the direction of the roll axis and which are each formed by a piston in cylinder unit actuated by pressure fluid to exert a supporting force on the inner side of the roll jacket. A device for influencing the roll temperature via at least one fluid flow separate from the pressure fluid charging of the support elements is provided, with the support elements controllable individually and/or group-wise. In this manner, corresponding roll zones follow one another in the direction of the roll axis. Such a roll is described, for example, in EP-B-0 328 503.
2. Discussion of Background Information
In deflection controlled rolls or deflection compensation rolls, support sources or support elements are used which are charged with oil pressure via a supply line. The respective support source is pressed toward the rotating roll jacket by this oil pressure. Since the piston surface of the support source is smaller than the hydrostatic pocket surface facing the roll jacket, a lower pocket oil pressure is adopted. The pressure difference between the piston pressure and the pocket pressure defines the volume flow which flows via the capillaries disposed between the pocket surface and the piston surface. The respective volume flow is thus adopted at a support source in dependence on the piston pressure.
The support sources are individually charged with an oil pressure for an individual profile correction, i.e. in particular for the correction of certain transverse property profiles of the goods web, in particular of a paper web or of a cardboard web, running through the roll nip. The level of the oil pressures is regulated via an online profile thickness measurement of the goods web.
Large differences can occur between the oil pressures of the different support sources (e.g. from 3.5 to 90 bar from support source to support source) in dependence on the respectively required profile corrections. As already indicated, this results in volume flow differences at the support sources. Friction occurs between the rotating roll jacket and the support sources due to the oil shear in dependence on the jacket speed and to the oil gap level, which is in turn dependent on the volume flow, on the oil temperature and on the pocket pressure. Thus, a friction level results with a different amount from one support source to the other as a consequence of the large pressure differences and is expressed in temperature differences at the roll jacket. These temperature differences in turn have an effect on the shape of the roll jacket and thus also produce a feedback effect which influences the produced path load profile of the deflection controlled roll.
Since a lower volume is adopted with a pressure balance at a support source, a higher temperature results at this support source despite an operationally lower friction level than with higher pressures. A higher temperature now, however, results in an expansion of the roll jacket which is expressed in a path load increase in the roll nip. The temperature development is therefore expressed in the reverse direction to the desired pressure balance and is thus unwanted. In individual cases, this can even result in instability in the control behavior.
Usually, the temperature development at the support sources is limited by a separate cooling oil flow which is led into the inner space of the roll. For this purpose, a volume flow of lower temperature is distributed in the inner space of the roll via nozzles, the amount of said volume flow being controlled via the return temperature of the roll. Up to now, the same amount of cooling oil is supplied to each support source by such a distribution. However, as a consequence of the previously named volume flow differences, different temperatures are adopted at the support sources despite the supplied cooling oil amount. This state of affairs is documented by the following calculation example:
The present calculation example is a deflection compensation roll of a thickness calender, with the production speed amounting to 1540 m/min. The surface temperature of the roll is, in this case, equal to the return temperature so that no heat flow flows through the jacket.
The technical data relevant to the calculation are as follows:
The temperature development and the friction level of a support source were examined in the calculation for a minimum (3.5 bar) and a maximum (90 bar) possible piston pressure in dependence on the cooling flow.
FIG. 1 shows a diagram in which the respective oil temperature resulting after a support source is shown over the secondary flow, i.e. the cooling flow, for the minimum and the maximum piston pressure of 3.5 bar and 90 bar respectively. In this connection, the temperature is given in xc2x0 C. and the secondary flow in ltr./min. The oil temperature shown was determined directly in the outlet in the direction of jacket rotation behind the support source.
In the inlet of the support source, oil is taken in underneath the support source with the running of the roll jacket at a mixed temperature which results from the injection of the cooling oil into the interior of the roll.
It can be recognized from FIG. 1 that the oil temperatures are much higher for all examined cooling oil flows at a piston pressure of 3.5 bar than at a piston pressure of 90 bar.
The mixed temperature adopted at the interior of the roll approximately corresponds to the local return temperature. FIG. 2 shows a diagram in which the calculated return temperature is entered over the cooling flow (secondary flow) in each case for the two different piston pressures. In this connection, it must be noted that in each case only one support source was examined in the calculation, i.e. a mixing of the oil from a plurality of support sources with different oil pressures and thus different temperatures remains unconsidered.
The adopted local return temperatures show an increasing temperature difference between a support source with a high load and a support source with a low load as the cooling flows become smaller. Such a temperature difference, however, now has a decisive effect on the shape of the rotating roll jacket.
The present invention provides an improved deflection controlled roll of the kind initially mentioned in which the above-mentioned problems have been eliminated.
According to the invention, a respective local charging of the different roll zones takes place by the temperature influencing device in dependence on the piston pressure of the support element or of the support element group of the respective roll zone.
Not only an optimum temperature homogenization is possible due to this design, but the fluid flow required to influence the roll temperature is also reduced.
In a preferred embodiment of the deflection controlled roll in accordance with the invention, at least some of the roll zones can be charged in each case with a cooling fluid, in particular with a cooling oil, by the temperature influencing device.
Generally, however, such a design is also conceivable in which at least some of the roll zones can each be charged with a heating fluid by the temperature influencing device, with oil preferably also again being used in this case.
In an expedient practical embodiment of the deflection controlled roll in accordance with the invention, the fluid amount locally associated with a respective roll zone by the temperature influencing device can be varied in dependence on the piston pressure of the relevant support element or of the relevant support element group.
The annular spaces of the different roll zones provided between the roll jacket and the yoke can advantageously be charged with the relevant fluid by the temperature influencing device.
The temperature influencing device can in particular include nozzles via which the relevant fluid can be injected into the respective roll zones. In this connection, a valve is preferably respectively disposed before the nozzles via which the respective fluid amount can be controlled in dependence on the respective piston pressure. The valve can in particular be designed such that it increasingly closes as the piston pressures become increasingly higher and vice versa.
In an expedient practical embodiment of the deflection controlled roll in accordance with the invention, in which in particular cooling fluid is used, the valve is designed and/or controllable such that it is at least substantially fully closed at piston pressures above a pre-settable upper limiting value and/or at least substantially fully open below a pre-settable lower limiting value.
An expedient practical embodiment is characterized in that the valve cross-section can be varied via a spring-loaded valve body which can be charged against the spring force by the piston pressure.
A constant mixed temperature at the interior of the roll can thus in particular be produced by a design of the nozzle cross-section matched to the support source size.
For the initially stated case, this means that, for example, only about 1.7 ltr./min. of cooling oil is sufficient for a support source with 3.5 bar piston pressure in order to achieve the same return temperature of a support source with 90 bar without cooling oil. Without such a volume flow control, a substantially higher cooling oil amount would have to be supplied to obtain the same mixed temperature. It is also no longer necessary, as in the previously described case, to lower the return temperature of all support sources to an unnecessarily low amount so that, moreover, the drive power of the roll can be kept low. An alternative raising of the inlet temperatures to avoid this problem would further increase the total volume flow of the roll.
The solution in accordance with the invention thus provides the advantage of a reduction in the required cooling fluid flow in addition to the advantage of a temperature homogenization.
An alternative advantageous embodiment of the deflection controlled roll in accordance with the invention is characterized in that a variable steering of a fluid volume flow supplied locally to a respective roll zone by the temperature influencing device is provided which is controlled in dependence on the piston pressure of the relevant support element or of the relevant support element group. In this connection, the steering of the fluid volume flow can in particular be controlled by the piston pressure itself. The steering of the fluid volume flow can take place via variable metal sheets, for example.
In an expedient practical embodiment, the fluid delivered by the temperature influencing device is supplied to an annular space enclosing the pocket region of the respective hydrostatic support element. This produces the advantage that the fluid serving for the temperature influencing can be supplied independently of the direction of roll rotation via a supply line. To keep the pressure in the annular space or the annular passage and the friction as low as possible, the width of the web outwardly bounding the annular space is much smaller than the width of the web provided between this annular space and the pocket region. The further advantage thus results that, even with a roll made completely empty, sufficient fluid is available in the inlet of the support source which is brought in at high speed beneath the support source.
The present invention is directed to a deflection controlled roll that includes a rotating roll jacket, a rotationally fixed yoke arranged to axially pass through the roll jacket, and a plurality of hydrostatic support elements arranged on the yoke in a direction of a roll axis which are chargeable with a pressure fluid to exert a supporting force on an inner side of the roll jacket. A device for influencing a roll temperature via at least one fluid flow, which is separate from the pressure fluid is also included. The support elements are arranged into a plurality of controllable roll zones arranged along the roll axis. The temperature influencing device is structured and arranged to locally charge respective roll zones depending upon a pressure on the support elements in a respective roll zone.
In accordance with a feature of the invention, the support elements can be arranged in series along the roll axis.
According to another feature of the present invention, the support elements can include piston in cylinder units. Each roll zone can include an individual piston in cylinder unit and the local charging of each roll zone may depend upon the piston pressure. Further, the support elements may be structured and arranged to be individually controllable. Moreover, each roll zone can include a group of piston in cylinder units, whereby the local charging of each roll zone depends upon the piston pressure of the group. The groups may be structured and arranged to be individually controllable.
In accordance with still another feature, the temperature influencing device can be structured and arranged to charge at least some of the roll zones with a cooling fluid. Additionally, or alternatively, the temperature influencing device can be structured and arranged to charge at least some of the roll zones with a heating fluid.
The temperature influencing device may be structured and arranged to supply a varied fluid amount to each the roll zone depending upon the on the support elements.
Further, the at least one support element may include a piston in cylinder unit and the temperature influencing device may be structured and arranged to supply a varied fluid amount to each the roll zone depending upon a piston pressure.
The roll jacket and yoke can be arranged to form an annular space, and the temperature influencing device may be arranged to charge the annular space for the at least one roll zone with the at least one fluid flow.
The temperature influencing device can include nozzles structured and arranged to inject the at least one fluid flow into the at least one roll zone. Further, the at least one support element can include a piston in cylinder unit and a respective valve position before each of the nozzles and a respective fluid flow amount may be controllable depending upon piston pressure. A respective valve can be positioned before each of the nozzles and a respective fluid flow amount may be controllable depending upon a respective piston pressure. The respective valve can be structured to increasingly close as piston pressure becomes increasingly higher, and the respective valve can be structured to increasingly open as piston pressure becomes increasingly lower. Further, the respective valve may be structured to be controllable such that it is at least one of: at least substantially fully closed at a piston pressure above a pre-settable upper limiting value and at least substantially fully open at a piston pressure below a pre-settable lower limiting value. Still further, a cross-section of the respective valve may be variable via a spring-loaded valve body which can be charged against a spring force by the piston pressure. A cross-section of the respective nozzle can be matched to a size of a respective support element in order to produce a constant mixed temperature at an interior of the roll jacket.
Still further, the respective valve can be structured to increasingly close as pressure on the support elements becomes increasingly higher, and the respective valve is structured to increasingly open as pressure on the support elements becomes increasingly lower. Also, the respective valve can be structured to be controllable such that it is at least one of: at least substantially fully closed at a pressure above a pre-settable upper limiting value on the supporting elements and at least substantially fully open at a pressure below a pre-settable lower limiting value on the support elements. Moreover, a cross-section of the respective valve can be variable via a spring-loaded valve body which can be charged against a spring force by the pressure on the support elements to support the roll jacket. A cross-section of the respective nozzle may be matched to a size of a respective support element in order to produce a constant mixed temperature at an interior of the roll jacket.
According to still another feature of the present invention, the temperature influencing device can be arranged to controllably and locally supply a variable steering of the fluid flow to respective roll zone depending upon a pressure on the at least one support element supporting the roll jacket.
Further, the at least one support element may include a piston in cylinder unit and the steering of the fluid flow is controlled by piston pressure.
According to another feature, the steering of the fluid flow may take place via variable guide plates.
The at least one support element can include an annular space surrounding a pocket region, and the fluid flow supplied by the temperature influencing device can be supplied to the annular space. A width of a web outwardly bounding the annular space may be smaller than a width of a web located between the annular space and the pocket region.
In accordance with still yet another feature of the present invention, at least one of the pressure fluid and the fluid flow comprises oil.
The invention is directed to a process for operating a deflection controlled roll that includes a rotating roll jacket, a rotationally fixed yoke arranged to axially pass through the roll jacket, and a plurality of hydrostatic support elements arranged on the yoke in a direction of a roll axis. The process includes arranging the plurality of hydrostatic support elements into a plurality of controllable roll zones along the roll axis, charging the plurality of hydrostatic support elements of each controllable roll zone with a pressure fluid to exert a supporting force on an inner side of the roll jacket, and supplying at least one fluid flow, which is separate from the pressure fluid, into each controllable roll zone depending upon a pressure on the plurality of hydrostatic support elements in a respective controllable roll zone.
In accordance with still yet another feature of the present invention, the hydrostatic support elements can include piston in cylinder units, and the process may further include supplying the at least one fluid flow depending upon the piston pressure. The piston pressure and the at least one fluid flow supply are inversely proportional.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.